Add chart components 216-245; step-aware ticks, font-aware labels

Bars, lines, areas, pies, donuts, radar, histogram, scatter, bubbles,
heatmaps, gauge, bullet, funnel, waterfall, treemap, candles, box
plots, steps, rings, legend, axis, crosshair, polar area, pyramid,
spectrum bars and win-loss strips, each drawn dot by dot. Ticks follow
1-2-5 steps and print as precisely as their step needs; a label row
uses micro letters or the pixel font as a whole. Descriptions carry the
data in numbers. Bad data panics.

chart/horizontalbar.go

@@ -0,0 +1,44 @@
+package chart
+
+import (
+	"fmt"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type HorizontalBarOptions struct {
+	// Width is in dots, zero means 160; rows are lines.
+	Width int
+	// Slot fills the bars; zero means Accent.
+	Slot pixel.Slot
+}
+
+// HorizontalBar lays labeled bars across, longest to the edge.
+func HorizontalBar(c *ui.Context, text string, labels []string, values []float64, o HorizontalBarOptions) *ui.Element {
+	k := pixel.K(c)
+	if len(labels) != len(values) || len(values) == 0 {
+		panic(fmt.Sprintf("chart: HorizontalBar has %d labels for %d values", len(labels), len(values)))
+	}
+	w := pixel.Or("HorizontalBar Width", o.Width, 160)
+	lo, hi := span(values)
+	if lo < 0 {
+		panic(fmt.Sprintf("chart: HorizontalBar value %v is negative", lo))
+	}
+	gutter, room := 0, 0
+	for i, l := range labels {
+		gutter, room = max(gutter, pixel.Measure(l)), max(room, tinyW(num(values[i])))
+	}
+	ink := pick(o.Slot, 0)
+	return ui.Box(c).Size(k.D(w), k.D(len(values)*pixel.LineHeight)).Role(ui.RoleImage).Label(text).Description(read(labels, values)).Draw(func(pt *ui.Painter, r ui.Rect) {
+		g := k.Canvas(pt, r)
+		span := w - gutter - room - 8
+		for i, v := range values {
+			y, bw := i*pixel.LineHeight, int(part(v, hi)*float64(span))
+			g.Text(gutter-pixel.Measure(labels[i]), y, labels[i], pixel.Faint, 1)
+			g.Rect(gutter+4, y+4, max(1, bw), pixel.LineHeight-8, ink)
+			tiny(g, gutter+6+bw, y+6, num(v), pixel.Ink)
+		}
+	})
+}